Solar Energy Generating Systems (herein referred as “SEGS”) are electricity producing systems that utilize solar energy as a source heat which coupled with a Rankine engine transform thermal energy into shaft energy which gets transformed into electrical energy. The fluid heated by the sun in a solar collector is used to evaporate a working fluid and the vapor is used to move a turbo-generator by conventional techniques. The spent vapor is condensed utilizing either cold water or air as a heat sink. The turbines of the Rankine engine are a well known and mature technology and latest improvements are relatively small, but there is potential for improvement in the solar collector field which today represents the bulk of the investment of SEGS.
Efforts to capture solar energy to produce steam are more than 150 years old (August Mouchot—1860). Sun-tracking parabolic reflectors are more than 100 years old. Frank Shuman applied for U.S. Pat. No. 1,240,890 in Sep. 30, 1912 for a Sun Boiler that comprises, among other things, a sun tracking parabolic collector. The oil embargo in 1973 spurred research efforts to develop renewable energy sources which translated into a deluge of patents and papers with leap jumps in improvements and installation of photovoltaic panels, wind turbines and solar thermal systems. Several SEGS large plants were installed in the Mojave Desert in the 1980s with a combined capacity of 354 MW.
Recent high energy prices have sparked renewed interest in the use of renewable energy sources. Solar energy, available almost everywhere, is unfortunately much diluted and fluctuates widely during the year and even during the day, even without taking into consideration cloud cover. The installation of wind turbines and photovoltaic has exploded in the last decade and prices have continued to drop, but due to their unsteadiness and unpredictability, without storage, they are not able to provide the steady electricity we need.
The new SEGS with better trough parabolic mirrors and solar towers with dual axis tracking heliostats operating at higher temperatures and with molten salts as thermal storage are able to provide steadier generation and are becoming less pricey. Progress has been impressive and efficiencies have improved steadily over time with better materials, better tracking mechanisms, evacuated tubes, the use of thermal oils and molten salts, or even new approaches like Stirling engines mounted on top of parabolic dual tracking mirrors. Yet, challenges remain
State-of-the-art, sun tracking trough parabolic collectors are oriented along the North South (“NS”) axis, with the mirror and receiver following the sun's movements from East to West, but are held horizontally even when it is well known that inclining the mirror will allow the capture of more energy. There are two problems with NS orientation: (i) the sun's altitude also changes during the day and seasons (in the winter months in most of the USA, the sun does not rise above the horizon more than 40°, and therefore, collectors oriented along the NS axis face substantial dispersion due to the cosine law in the winter), and; (ii) inclining the collectors to capture more energy is prevented from (a) wind considerations that requires a strong structure to prevent damage to a large moving area; (b) shadowing effects requiring large distances between collectors, and even; (c) possible freeze considerations due to the difficulty of draining low spots of a field of inclined collectors. As of today, no economic solution has been found for the problem of inclining large surface collectors capable of resisting strong winds.
An inclined collector oriented along the East-West (“EW”) axis, facing South in the northern hemisphere ameliorates some of the problems discussed above, but encounters others. The hourly movement of the sun produces accentuated daily dispersion and the collectors need to be spaced further apart. While the output of NS collectors peaks during the summer, the output of inclined EW collectors (same angle as latitude) peaks during the spring and fall equinoxes.
Since the electricity generated is mostly sold to utilities, to improve the financial viability of SEGS, developers sought larger solar thermal installations to capture better economies of scale, high temperatures to improve thermal efficiencies and even molten salts to provide some storage, that has resulted in increased size and complexity which makes their financing and proliferation difficult.
The present invention relates to the use of an inclined and flip-able spiral shaped fixed trough collector, oriented along the EW axis with a moving receiver. The system departs from current pursuit of high temperature and large generation units, seeking instead a less costly and simpler smaller scale system, which could be the basis of a distributed system generating with capacities of several hundred kW.